404 General Notes. L^ay, 



its skin to dcssication. The question naturally arises, could such 

 a creature ever become habituated to living on land ? When we 

 remember that the skin of the leech performs the function of lungs, 

 and that, provided it is kept wet, it is capable of drawing its sup- 

 ply of oxygen from moist air, there is no difficulty in understand- 

 ing how such a change might be induced. Experiment has 

 already shown that some water-breathing animals can without 

 difficulty become air-breathers. The Mexican axolotl is a well 

 known instance, and the Lymnseidae which belong to the deep 

 water fauna of the Lake of Geneva form another. Nature herself 

 supplies us with numerous examples in which such a change is a 

 normal occurrence in the animal's cycle of life. No one has un- 

 dertaken to test the matter in the case of the leech ; but there is 

 every reason to believe that nature has made this experiment, and 

 that the land-leech found on the mountains of this island, and in 

 some other parts of the world, is a living demonstration of her 

 success. In this country the land-leech is found near the tops of 

 mountains, in dense thickets, where the ground is carpeted with 

 moss and other low plants. During the dryest months of sum- 

 mer, these localities are kept moist by mists and showers. The 

 structure of the leech has been modified to some extent in accom- 

 modation to its pre.sent mode of life, but this modification is in 

 every particular one of adaptation. Not an organ has been lost or 

 acquired, certain organs have been compelled to do more work in 

 the land-leech than they do in the common leech, and the natural 

 result has been multiplication and enlargement. The skin-glands 

 have become larger and more numerous, and the urinary vesicles 

 have expanded into bladder-like reservoirs. The liquid secretions 

 of these organs supply any deficiency of water in the air, enabling 

 the leech to keep its dermal respiratory organ constantly moist. 



The land planarian forms also are interesting examples of the 

 kind here considered. This worm, which creeps about in damp 

 weather, somewhat like a slug, is abundant in this island, and in 

 many of the islands to the south. It has a wider distribution than 

 the land-leech, being found in nearly all temperate and tropical 

 zones, not only on islands, but also on the continents, where the 

 moisture of island atmosphere prevails. 



There is another very remarkable case, allied in some respects 

 to those just mentioned. What could seem more out of place 

 than a fish on land! It would seem that fishes are especially 

 adapted to live exclusively in water. In providing the fish with 

 fins, and with a respiratory organ in the form of gills, nature 

 seems to have decreed that one class of animals should have a 

 place and keep it. But all her devices to keep certain members 

 of the finny tribe within the prescribed medium have failed. 

 Among those remarkable fishes 'which have succeeded in over- 

 coming every obstacle to living out of water, at least one very in- 

 teresting species occurs on the coasts of Japan. This is the 



